For example, moving objects such as automobiles are equipped with various electronic control units (ECUs) for controlling various types of devices. These ECUs are connected to, for example, a network such as a controller area network (CAN) to control the automobile while transmitting/receiving signals through the network.
In a network that electronic apparatuses such as ECUs are connected to, ensuring the validity of communication is extremely important in order to prevent wrong control. In order to ensure the validity of communication, the use of encryption techniques is effective. For example, if electronic apparatuses performing communication share data such as shared encryption keys correctly, this data can be used to authenticate communication, conceal contents of communication, and detect tampering. However, when another electronic device improperly acquires the data to be shared between the electronic apparatuses that perform communications, validity of communications cannot be guaranteed.